Techniques for Open Shell Calculations for Atoms
As in nonrelativistic atomic structure theory1–6, angular momentum plays a big part in the construction of n-electron states and of simplifying the matrices of operators in the relativistic theory7. Racah algebra, second quantization, and diagram techniques, discussed in the references just mentioned, all play a part in deriving general purpose expressions which are suitable for implementation in a computer program. Some aspect of this work, which have been important in developing one system of relativistic atomic structure programs8 incorporating radiative corrections9 will be described in this lecture. Of course, this approach, which depends heavily on the use of Dirac central field orbitals, has little to offer those wishing to study molecular structure, where symmetry has less of a dominant role. It is also fair to point out that Desclaux10 uses algorithms based on somewhat different principles; it is encouraging that nevertheless, results from both systems of programs are in close agreement.
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